CHARACTERIZATION OF NUCLEAR RIBOSOMAL DNA (RDNA) IN GAEUMANNOMYCES-GRAMINIS AND CORRELATION OF RDNA VARIATION WITH G-GRAMINIS VARIETIES

Analysis of nuclear ribosomal(r) RNA genes in Gaeumannomyces graminis has revealed two levels of variation: one allowed identification of G. gramminis varieties and the other enabled discrimination between isolates within varieties. The three varieties, G. graminis var. graminis (Ggg), var. avenae (Gga) and var. tritici (Ggt) could be differentiated based on the size of an EcoR I fragment, a Hind III-EcoR I fragment and a Hind III-Pst I fragment from the 26S rRNA coding region. Within the collection of isolates identified as Ggt on morphological criteria, three subgroups (T1, T2 and T3) could be distinguished based on the size of the three fragment types from the 26S rRNA coding region. The sizes of the three fragment types also distinguish Ggg, Gga and Ggt (subgroup T1). Ggt (subgroup T2) possesses large amounts of the Hind III-Pst I fragment that is typical of Gga and trace amount of the Hind III-Pst I fragment characteristic of Ggt (subgroup T1). Ggt (subgroup T3) possesses all the three fragments that marked Gga and none of Ggt (subgroup T1). All isolates in T2 and T3 were pathogenic to wheat, oats and bentgrass. Isolates within each variety could be differentiated by restriction site differences in the intergenic spacer region and by variation in repeat length.